The invention is directed towards a dielectric member for interposition between a first electrical component, such as an electrical socket, and a second electrical component, such has a printed circuit board, which has a preselected coefficient of thermal expansion (CTE) that relieves existing CTE mismatches between first and second electrical components.
Interfaces between separate electrical components which are subjected to thermal cycling typically experience stresses caused by the different rates of expansion and contraction of each electrical component. For example, a first electrical component may have a low CTE while the second electrical component has a relatively higher CTE, indicating a greater degree of thermal expansion and contraction. In particular, electrical connectors mounted to printed circuit boards virtually always have higher CTE values than the printed circuit boards on which they are mounted. This CTE mismatch results in a relative motion between the first and second electrical components at their interface.
One arrangement which is particularly subjected to CTE mismatch is a microprocessor housed in a socket and mounted on a printed circuit board. In this arrangement, the components are subjected to extreme thermal cycling. The microprocessor generates heat during operation that is transferred to the electrical socket which houses the microprocessor. Because of the difference in base materials between the microprocessor and the electrical socket (the processor is typically made from a ceramic or resin material while the electrical socket is molded from an insulative plastic) a CTE mismatch is encountered at the processor/socket interface. The CTE mismatch at this interface is typically not problematic because there are no rigid points of electrical connection (e.g., solder joints) between the processor and the socket. Therefore, the difference in thermal expansion and contraction between the socket and the processor may be absorbed by the relatively tolerant electrical connections between the socket and the processor.
However, the electrical socket is typically soldered to a printed circuit board in a through-hole or surface mount configuration which requires rigid and relatively inflexible solder joints. And, as with the processor and the socket, the printed circuit board is subjected to fairly extreme thermal cycling which is also transferred to the electrical socket. Typical CTE values for printed circuit board materials fall between the range of 12 and 18 ppm/xc2x0 C., which indicates relatively little expansion and contraction when subjected to thermal cycling. On the other hand, a molded electrical socket manufactured from an insulative plastic material may have CTE values ranging from approximately 15 to 70 ppm/xc2x0 C. These CTE values indicate that the processor socket will expand and contract at a greater rate than the printed circuit board when subjected to thermal cycling. As a result, rigid electrical connections such as solder joints between the processor socket and the printed circuit board are subjected to induced stresses which frequently cause solder joints to fracture thereby causing electrical failure at the joint.
Efforts have been taken by electronics manufacturers to enhance or reinforce solder joints at the socket/pcb interface to prevent fracture and resulting electrical failure. However, these efforts too can produce unreliable results. For instance, it is difficult to ensure uniform solder joints when a large array of electrical contacts is used. This problem is frequently manifested in the occurrence of solder-wicking. Solder-wicking occurs when, by capillary action, solder flows along the electrical contact and away from the desired point of electrical interconnection. This results in a weaker, less reliable solder joint.
Accordingly it would be desirable to provide a way of accommodating or minimizing the effect of CTE mismatches between separate electrical components such as a processor socket and a printed circuit board. It would also be desirable to improve the reliability of solder joints between electrical components by improving their uniformity and inhibiting occurrences of solder-wicking.
In accordance with the objects of the present invention, a socket for receiving a semi-conductor package is provided having a housing with a plurality of electrical contacts. A dielectric is provided having a plurality of first conductive sites exposed on a top surface of the dielectric and a plurality of second conductive sites exposed on a bottom surface of the dielectric. The first and second conductive sites are electrically interconnected. The plurality of electrical contacts are electrically connected to the first conductive sites while the second conductive sites are connected to an electrical component.
A dielectric member for interposition between a first electrical component and a second electrical component is provided. A plurality of electrically conductive members are held within the dielectric member having an exposed top surface and an exposed bottom surface for electrical connection with the first electrical component and the second electrical component, respectively.